Astronomers have known for a while that distant dwarf irregular galaxies have reservoirs of neutral hydrogen gas, the key material required for formation of stars, but were puzzled that neighboring dwarf galaxies didn’t seem to have much hydrogen gas. New research published on Thursday, October 16th highlights that the Milky Way galaxy stripped all of the neutral atomic hydrogen “star fuel” from neighboring galaxies billions of years ago.
Milky way is part of a group of gravitationally bound galaxies
The Milky Way galaxy is actually the largest member of a compact clutch of galaxies that are bound together by gravity. Swarming around our home galaxy is a menagerie of smaller dwarf galaxies, the smallest of which are the relatively nearby dwarf spheroidals, which may be the leftover building blocks of galaxy formation. Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies, which are not gravitationally bound to the Milky Way and may be relative newcomers to our galactic neighborhood.
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More on the new research
Earlier studies showed that unlike far-away dwarf galaxies, nearby dwarf galaxies did not seem to have much atomic hydrogen, but the methods for making observations were not sensitive enough to completely rule out the presence of hydrogen in the dwarf spheroidal galaxies.
This new research utilizes the combined power of the National Science Foundation’s Green Bank Telescope in West Virginia (the world’s largest fully steerable radio telescope) and a number of other powerful telescopes from all around the globe. With this viewing power, the researchers were able to carefully analyze the dwarf galaxies close to the Milky Way for even tiny amounts of atomic hydrogen. Lead author Kristine Spekkens, assistant professor at the Royal Military College of Canada, explains:
What we found is that there is a clear break, a point near our home galaxy where dwarf galaxies are completely devoid of any traces of neutral atomic hydrogen.
The break point occurs around 1,000 light-years from the edge of the Milky Way’s disk to a point that is thought to coincide with the edge of its dark matter distribution, and beyond this point hydrogen gas-rich, dwarf irregular galaxies are again commonplace.